Epitaxial growth of crystals will be understood to mean growth in which crystal structure of one crystal extends smoothly into an adjacent crystal. In the prior art, only compounds the lattice constants of which were equal or nearly equal were thought to be suitable for epitaxial growth.
The purpose of epitaxial crystal growing has been to provide extremely high quality crystals comprising layers of different chemical composition, for use in transistors, other semiconductor devices are integrated optics devices. It has been found that nonepitaxial crystal growth produces crystals with cracks, voids and other defects that impair the operation of these devices and result in their eventual failure.
Because nonepitaxial crystals were unsatisfactory, and epitaxial growth was thought to be restricted to combinations of materials with lattice constants that matched exactly or nearly so, the prior art was unable to combine chemical compounds that, otherwise, could offer promise of improved performance in a wide variety of applications. In particular, in the field of integrated optics, it has not previously been possible to combine III-V compounds for semiconductor devices and garnets and other magnetically suitable materials, and therefore it has not been possible to combine magnetic and electric devices on the same substrate. In the manufacture of electrical devices, also, the method taught by this invention will offer better choices of the materials.
One prior art method of combining materials of different lattice constants is disclosed in U.S. Pat. No. 4,032,951 issued to J. C. DeWinter et at on June 28, 1977, that discloses a method of epitaxial growth in which a layer of graded chemical composition forms a transition zone between two crystals of different lattice constants.